Align Grease Pencil with Camera Angle
The grease pencil strokes are aligned to the window in which you draw. Strokes will appear in a plane that is perpendicluar to the Z axis of the camera (or to whatever other view you want to draw in).
Here is an example that shows how to draw in camera view (press Numpad 0).

The distance to the camera, in which the grease pencil layer appears, is determined by the placement of the 3D cursor.


Note that the link posted on the question refers to the annotation tool, which is a different tool than the Grease Pencil